摘要:

In a portion of the visible and near-infrared spectrum (0.40-0.85 μm), high resolution (0.002 μm) reflectances from 37 soil samples have been analysed to determine complex refractive indices and the mean radius of soil particles. The method uses an approximation to a radiative transfer model. The approximation assumes that measured spectral reflectances and the imaginary refractive index can be expressed as quadratic functions of wavelength. Using this approximation, three quantities, the real refractive index, the particle radius, and a constant relating to the imaginary index are derived from wavelength coefficients for measured reflectance spectra. The resulting values of particle radius generally increase with an increase in the median radius, which is measured in the laboratory. The complex refractive index is in general agreement with that estimated by using the previously developed analytic model. The spectral reflectance measured strongly depends on the product of the imaginary index and particle radius identified by the approximation, but does not depend on those separately. Based on results of a regression analysis, the imaginary index and particle radius are useful in explaining variations in soil components, which have a major influence on soil colour, such as humus and free Fe2O3.

ISSN:0143-1161    

DOI:10.1080/01431169608948763

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The ER-2, with the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) onboard, overflew Rapid City, South Dakota, and the United States Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Site, Oklahoma, on 9 August and 15 August 1993, respectively. High contrast natural and artificial surfaces present in the imagery were used as a basis for retrieving aerosol spectral optical depth (SOD) over these two sites. Coincident measurements of spectral optical depth from a surface-based sunphotometer also were obtained and used as a validation of the AVIRIS derived retrievals. The accuracy of the retrievals is discussed as a function of measurement uncertainty and surface contrast. The results indicate that, given sufficiently small sensor errors and spectrally uniform surfaces with a reflectance difference of at least 0.5, aerosol spectral optical depth over clear continental atmospheres can be retrieved from high spatial resolution space-based imagery to an accuracy of approximately 0.1. Although only two cases are reported here and additional tests are required, these preliminary results suggest that background aerosol spectral optical depth (i.e., τaerosol, <01) cannot be retrieved with adequate accuracy from space; however, the aerosol spectral optical depth of more polluted atmospheres (i.e., τaerosol< 0.2) can be retrieved with adequate accuracy.

ISSN:0143-1161    

DOI:10.1080/01431169608948764

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The primary purpose of airborne laser altimetry is to determine the ellipsoidal or geoidal coordinates of a series of points on the surface of the Earth. An aircraft that is instrumented with a laser altimeter, an inertial navigation system, and a Global Positioning System (GPS) receiver provides the following data: (1) laser range to the Earth's surface, (2) measurement platform spatial location and orientation, and (3) aircraft kinematic trajectory in ellipsoidal coordinates. These data are sufficient to determine (georeference) the three dimensional coordinates of the points where the beam from a pulsed laser intersects the Earth. We develop the exact equations necessary to georeference the laser points. We also discuss calibrating the laser pulse timing, laser positioning and alignment relative to the local-level reference frame, correcting atmospheric refraction effects on the laser pulse, and time synchronizing the various data streams. We use a laser altimeter mission flown over Lake Crowley in California to demonstrate our methods. For seven passes over the lake, our heights agreed with a local tide gauge at the Lake Crowley dam to better than 10 cm with standard deviations ranging from 1-4 cm. The horizontal accuracy of the georeferenced points is still problematic; we have no three-dimensional control points that the laser has hit. Geometrical considerations indicate that the measured horizontal location of the laser footprint is within two metres of the true location when the aircraft altitude is less than one kilometre above the local surface.

ISSN:0143-1161    

DOI:10.1080/01431169608948765

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

This paper shows the advantages of post-processing spectral classifications in a Geographical Information System (GIS) context in order to improve results. A maximum-likelihood algorithm was used to classify(both supervised and non-supervised) a Landsat TM sub-image in Central Mexico. Purely spectral processing yielded poor accuracy results, showing the spectral limitation to distinguish classes; as a consequence, merging classes was necessary in order to increase accuracy (from less than 55 to 82 per cent). GIS rules were finally applied based on ancillary data (terrain mapping units and elevation data) improving the final accuracy to 88.2 and 83.0 per cent (supervised and non-supervised classifications).

ISSN:0143-1161    

DOI:10.1080/01431169608948766

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431169608948767

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0143-1161    

DOI:10.1080/01431169608948768

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor